Recipe for bees: Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse.

Jan Baptista van Helmont’s recipe for mice: Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice.

SPONTANEOUS GENERATION

The hypothesis that some vital force contained in or given to organic matter can create living organisms from inanimate objects.

Believed then as much as you believe the Earth is round !!!!!!

The first true experiment?Open Jars with Meat

Closed Jars with Meat

Francesco Redi-1600s Italian scientist

Did this show that life did not come from non-life?

Even with different types of meat closed jars=no maggots

Maggots appear on meat!

Microscopes Invented

REVEALED A WHOLE NEW WORLD OF LIVING THINGS THAT APPEARED TO ARISE

SPONTANEOUSLY !!!!THEY WERE CALLED “ANIMALCULES”---WE

NOW KNOW THEM AS MICROORGANISMS----

Needhams’s Experiment—Eng clergy--1745

Broth left openTo air or vital force !!!!!

Microorganismsgrow—Broth spoils !

Boiling kills micro-organisms !!!!

Seal flask withCork stopper—Microorganisms

Appear !!

SPONTANEOUSGENERATION

EXISTS !!!!!

Broth left openTo air or vital

force if it exists !!!!!

Microorganismsgrow—Broth spoils !

Spallanzani’s Experiment—Italian Priest--1767

Seal flask withmelted glass---

Drew off airto create vacuum

Boiled broth

NOMICROORGANISMS

PEOPLE DID NOT BELIEVE HIM

HE SEALED OUT THE VITAL FORCE !!!!!!

The French Academy of Sciences sponsored a contest for the best

experiment either proving or disproving

spontaneous generation!!!

Pasteur’s Experiment 1859

French Chemist

Pasteur disproved spontaneous generation!

The French Academy of Sciences sponsored a contest for the best

experiment either proving or disproving spontaneous generation!!!

HE WON!!!

HERE ARE PASTEUR’S ORIGINAL FLASKS STILL ON DISPLAY AT THE

PASTEUR INSTITUTE IN PARIS

STILL FREE OF MICROORGANISMS

Terms to Know

Prefix for without? A-

Word for beginning? Genesis

Prefix for life? Bio

Biogenesis—Living things come from living things!

Abiogenesis—Living things can come from non-living things!

This is the same thing as spontaneous generation—living things can spontaneously generate from non-living things—like the recipes !!!!

Molecules of the Atmosphere Carbon Dioxide

Hydrogen Cyanide (HCN)

Oparin postulated that the infant Earth had possessed a strongly reducing atmosphere, containing methane, ammonia, hydrogen, and water vapor. In his opinion, these were the raw materials for the evolution of life.

Oparin, Aleksandr Ivanovich (1894-1980)

The Miller-Urey Experiment

Organic molecules appear here

These are the substances foundin Miller and Urey’s apparatus !

The formation of protocells

• The work of American biochemist Sidney Fox in 1992 showed how the first cells may have occurred.

• Fox produced protocells by heating solutions of amino acids.

• A protocell is a large, ordered structure, enclosed by a membrane, that carries out some life activities, such as growth and division.

• For food, the first prokaryotes probably used some of the organic molecules that were abundant in Earth’s early oceans. These would be heterotrophs !

• Over time, these heterotrophs would have used up the food supply.

The first true cells

• However, organisms that could make food had probably evolved by the time the food was gone. These would be autotrophs !

• These first autotrophs were probably similar to present-day archaebacteria.

The first true cells

• Archaebacteria (ar kee bac TEER ee uh) are prokaryotic and live in harsh environments, such as deep-sea vents and hot springs. Note the similarity to early Earth!!!!

The first true cells

The first true cells

• The earliest autotrophs probably made food by chemosynthesis rather than by photosynthesis.

• In chemosynthesis, autotrophs release the energy of inorganic compounds, such as sulfur compounds, in their environment to make their food.

Photosynthesizing prokaryotes

• Photosynthesizing prokaryotes might have been the next type of organism to evolve.

• As the first photosynthetic organisms increased in number, the concentration of oxygen in Earth’s atmosphere began to increase.

• Organisms that could respire aerobically would have evolved and thrived.

The endosymbiont theory

• Complex eukaryotic cells probably evolved from prokaryotic cells.

• The endosymbiont theory,proposed by American biologist Lynn Margulis in the early 1960s, explains how eukaryotic cells may have arisen.

• The endosymbiont theory proposes that eukaryotes evolved through a symbiotic relationship between ancient prokaryotes.

Prokaryote

Aerobic bacteria Mitochondria Cyanobacteria Chloroplasts

Animal Cell

Plant cell

A prokaryote ingested some aerobic bacteria. The aerobes were protected and produced energy for the prokaryote.

Over a long time, the aerobes become mitochondria, no longer able to live on their own.

Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments.

The cyanobacteria become chloroplasts, no longer able to live on their own.

The endosymbiont theory

The similarities of the mitochondrial and chloroplast organelles in the eucaryotic cell to an entire procaryotic cell are striking. They are membrane-bound structures that contain DNA, RNA, and the same kind of ribosomes. This has led many biologists to speculate on the evolutionary origin of the two organelles. Figure 2.31 summarizes some of the current thinking. The prevailing hypothesis is that certain bacteria came to be permanently associated (in symbiosis) with precursor procaryotic amoeboid cells, thus establishing the first true eucaryote.  

• New evidence from scientific research supports this theory and has shown that chloroplasts and mitochondria have their own DNA and ribosomes that are similar to the ribosomes in prokaryotes.

• In addition, both chloroplasts and mitochondria reproduce independently of the cells that contain them.

The endosymbiont theory